Prior art patent document published WO 2010/097456 A1 discloses a valve actuating device that is operated by compressed air. This device comprises a piston that converts the pressure of the compressed air into a larger pressure acting on an auxiliary fluid like lubricating oil that itself acts on a larger surface of an actuating element of the device. In other words, a limited pressure of the compressed air entering the actuating device is converted into a larger force that moves the actuating element of the device on a reduced stroke. That force acts against a stack of Belleville disk springs. The actuating device of this teaching results in a quick opening and closing of the valve. However for certain applications, like for UHP (Ultra High Purity) gases, more generally for gases that produce a substantial temperature increase during an adiabatic compression and that are likely to react exothermically (ignite and/or explode) further to that temperature increase, it can be desirable to achieve a progressive opening of the valve.